The conventional approach to power distribution grid voltage control is based on techniques developed about 70 years ago, one goal of which is to control demand (either raising or lowering demand). In recent years, highly complex and expensive systems have been required to implement improved effective voltage control and conservation voltage reduction (CVR) based demand reduction, one example of which is power distribution grid voltage control. Typically, utilities operate in a narrow band of 116-124 volts, even though level ‘A’ service allows for a range of 114-126 volts. The difficulty in adhering to a tight regulation band arises from normal fluctuations in incoming line voltage at the substation, as well as load changes along the feeder. These changes cause the line voltage to vary, with utilities required to maintain voltage for consumers within specified bounds.
The prior art volt-ampere reactive regulation devices (VAR) devices for voltage control (referred to as voltage and VAR control devices) may be split into several categories including: 1) prior art voltage and VAR control devices with slow responding capacitors and electromechanical switches; ii) prior art voltage and VAR control devices with medium response capacitors and thyristor switched capacitors; and iii) prior art voltage and VAR control devices with power converter based VAR control using Static VAR sources or static synchronous compensators (STATCOMs). Moreover, it should be noted that four-quadrant inverters can provide a combination of bidirectional, real, and reactive power that can be used to adjust power flows.
Such prior art voltage and VAR control devices are operative/utilized on the transformer “primary” side, slow and concentrated. Moreover, capacitors in the prior art voltage and VAR control devices are mainly used for power factor control when used by customers and for voltage control when used by utilities. For power factor control, the downstream line current must be measured. Capacitors and/or inductors may be switched on or off based on the line current to realize a desired overall power factor (e.g., typically at a value of unity). In the second case of voltage control used by utilities, capacitors are controlled based on: 1) local voltage measurements; 2) other parameters such as temperature; and/or 3) dispatches communicatively received from a control center. The control center may dispatch decisions regarding capacitor control based on information received from multiple points in the network.
Most capacitors of prior art voltage and VAR control devices are switched using electromechanical switches. The electromechanical switches are limited in switching speed and by life of the switches. Many electromechanical switches are limited to 3-4 switches per day. A response time of approximately fifteen minutes is often required to enable voltage control with prior art voltage and VAR control devices. During this time, the following steps may be performed: 1) sensing voltages locally; 2) communicating the sensed voltages to a centralized control center; 3) power and/or voltage modeling of the system at the centralized control center; 4) determining to take action based on the model and perceived potential improvements; and 5) dispatching one or more commands from the centralized control center to the prior art voltage and VAR control device to switch the capacitor. More advanced Volt-VAR Optimization or VVO systems are moving to such centralized implementations so they can try to optimize the profile of voltage along an entire distribution feeder and reduce infighting between prior art voltage and VAR control devices.